Armor Breaker

The Armor Breaker costs (20,000 BP to purchase) But it is unlocked by collecting all 30 Left Arms in the story mode. The in-game description is "Modeled after the 'Kabutowari' swords of feudal Japan, this blade offers both lethal cutting power and the chance to destroy armor with every hit, making it a great choice against heavier targets, including large UGs."